We are finishing up an arc flash study and found that breaker setting changes make a large difference in the incident energy. One of our conclusions is to change the instantaneous and short time delay to a lower value. The problem is this will create a coordination problem with downstream devices. On one hand, lower settings are safer. On the other hand the existing settings allow greater selectivity / reliability. Which way do people go on this decision??
Thanks!

We ran into that also. It is hard to convince people to change device settings for the rare event when someone works on equipment and sacrifice coordination and reliability of the system. We had a few places where lower settings helped out and we implemented these as part of our safety practice. Before a worker can open the equpment, the must lower the device settings up stream. When they are done, the put the settings back. This puts some burden on the worker, but it seems to be a safer practice.

2008 NFPA 70E - Proper Maintenance

I just received a copy of the ROP 2008 Pre Print of NFPA 70E and it states proper maintenance of devices is required to successfully predict the incident energy. This is an important issue!

Maintenance Switches

I believe most of the major manufacturers such as Cutler Hammer, Square D etc. now have equipment with maintenance switches. By flipping the switch, the devices revert to very low settings while live work is being conducted.

For the most part I have been able to achieve risk Category 1 calculations by dialing the instantaneous down, and yet preserve adequate margin between that setting and full load amps and max anticipated motor starting. It has worked.

This is on industrial plants using 480V secondary main power circuit breakers and the exposure is calculated for MCC's not attached to the transformer secondary main.

In one case we had to add cable length to achieve RC 1.

In the two locations where this was accomplished, basic plant PPE included one layer of rated nomex so RC 1 was not seen as restrictive.

For medium voltage gear we were able to achieve Risk Category 3 or 4, and again, for the few times they rack in or out breakers, putting on the arc blast suit was not considered restrictive.

Quick trip, best arc flash reduction switch on the market

http://www.utilityrelay.com/QUICK-TRIP_Page.html

If you have the temporary setting like L. Hamilton says. What kind of category you are gonna put on the equipment? How to impletment the warning?

2 labels, one for each mode